An Oklahoma school system is the first in the country to install bulletproof shelters in its classrooms.

Healdton Public Schools in Healdton, Oklahoma, installed seven bulletproof shelters at its elementary schools and two larger ones in its middle school, KOCO reported. Future plans call for adding the shelters to the system's high school.

System superintendent Terry Shaw said he tested the shelters by staying inside one while a bullet was shot at it from the outside.

"When you have an intruder on campus, to know that you have somewhere to go quickly for the safety of your students, it's very relaxing," Shaw told KOCO.

The secured spaces, made by Shelter-in-Place, can also be used as tornado shelters.

The shelters come as increased attention is being paid to school security in the wake of a deadly attack at Parkland, Florida's Marjory Stoneman Douglas High School on Feb. 14. Gunman Nikolas Cruz allegedly killed 14 students and three adults at the school before escaping. He was later apprehended by police and faces 17 counts of murder.